IMAGING ACTIVITY IN VISUAL CORTEX AT THE CELLULAR LEVEL

Tubby-like Proteins(TULP)是存在于所有多细胞生物体中的蛋白质家族。这些分子的特征是存在一个保守的羧基末端的“筒状结构域”，它与其他已知蛋白质没有序列同源性。Tubby或其他TULP的基因突变通常会导致三种疾病表型中的一种或多种：(1)肥胖--“Tubby”的名称由此而来；(2)视网膜退化；(3)听力损失。与管状蛋白突变相关的疾病表型清楚地表明这些分子在正常组织功能中发挥着至关重要的作用。虽然每个家族成员的表达模式都不同，但Tubby蛋白主要在神经系统中发现，所有已知的人类Tubby蛋白都在视网膜中表达。TULP1基因突变是导致14型视网膜色素变性(约占遗传性RP病例的5%)的原因，人类TULP2基因定位在19号染色体上视锥视杆视网膜营养不良基因的最小识别区域内。此外，TULP1基因突变与几种人类综合征有显著的相似之处，这些综合征会导致感觉神经性听力损失和视网膜退化，并伴随肥胖。尽管筒状蛋白具有明显的医学重要性，但目前还没有任何生物化学功能被归因于这个蛋白质家族的任何成员。为了确定Tubby和其他TULP的生化功能，从而了解它们在疾病中的作用，我们将使用X射线结晶学来确定Tubby的高分辨率三维结构。我们将根据与其他已知蛋白质的结构相似性，通过鉴定活性部位或辅助因子等化学功能，以及应用伴随的细胞生物学和生化研究，包括细胞和亚细胞定位研究，来确定Tubby的功能。这是一个“结构基因组学”方法的模型问题，用于鉴定与医学相关的蛋白质的功能。这种方法依赖于结构信息、表型数据和纯蛋白质的可用性所带来的经典生物学方法。最近三维结构数据库的大规模扩展应该会极大地促进这种方法的发展。

Tubby-like proteins (TULPs) comprise a family of proteins found in all multicellular organisms. These molecules are characterized by the presence of a conserved carboxy-terminal "tubby domain" that does not exhibit sequence homology to other known proteins. Genetic mutation of tubby or other TULPs often leads to one or more of three disease phenotypes: (1) obesity - from which the name "tubby" is derived, (2) retinal degeneration, and (3) hearing loss. The disease phenotypes associated with mutations in tubby-like proteins clearly indicate a vital role for these molecules in normal tissue function. While the expression pattern of each family member is distinctive, tubby proteins are found mainly in the nervous system, and all known human tubby proteins are expressed in the retina. Mutation of the TULP1 gene is the cause of retinitis pigmentosa type 14 (about 5 percent of inherited RP cases), and the human TULP2 gene maps within the minimal identified region for the cone-rod retinal dystrophy locus on chromosome 19. Furthermore, tubby mutants bear a remarkable similarity to several human syndromes that result in combined sensorineural hearing loss and retinal degradation, accompanied by obesity. Despite the clear medical importance of tubby-like proteins, no biochemical function has yet been ascribed to any member of this protein family. In order to identify the biochemical function of tubby and other TULPs -and to thus understand their role in disease - we will use X-ray crystallography to determine the high-resolution three-dimensional structure of tubby. We will identify a function for tubby based on structural similarities to other known proteins, by identification of chemical functionalities such as active sites or cofactors, and by the application of concomitant cell biological and biochemical studies, including cellular and sub-cellular localization studies. This is a model problem for a "structural genomics" approach to identification of function for a medically relevant protein. This approach relies on structural information, phenotype data, and classical biology approaches enabled by the availability of pure protein. This type of approach should be greatly facilitated by the recent massive expansion of the database of three-dimensional structures.